This invention relates to reciprocating slat conveyors of the type having a plurality of movable slats for conveying a load and, more particularly, to a reciprocating slat conveyor having a first set of slats for conveying a load and a second set of slats for lifting and holding the load while the set of conveying slats retract.
Reciprocating slat conveyors having a plurality of movable slats for conveying a load are now generally well known. They are used in a variety of applications and for conveying many different types of loads. Examples of reciprocating slat conveyors are disclosed by U.S. Pat. No. 2,973,856, granted Mar. 7, 1961, to Will E. Brooks; by U.S. Pat. No. 5,088,595, granted Feb. 18, 1992 to Olof A. Hallstrom; and by U.S. Pat. No. 4,793,469, granted Dec. 27, 1988 to Raymond K. Foster.
It has been discovered that reciprocating slat conveyors do not always function well when conveying palletized loads. With palletized loads, the pallets do not always remain balanced with their weight evenly distributed on the slats. The movable slats of a conveyor contact the bottom of the pallets at various contact points,about the pallets, rather than uniformly across the bottom surface of the pallets. Unfortunately, the contact points are not always evenly distributed across the conveyor slats. As a result, the advancing conveyor slats do not always advance the pallets in a uniform manner, and a retracting conveyor slat sometimes catch the pallets and rotates them. This can cause the load to become stuck or blocked on the conveyor. Consequently, reciprocating slat conveyors do not always convey palletized loads in a reliable and controlled manner.
With non-palletized loads, such as bulk loads and garbage, the distribution of the load remains relatively uniform across the conveyor slats and, thus, the conveyor slats can function to convey the load in a uniform, controlled manner. However, with palletized loads, especially with older, used pallets, which can become bent or warped, the pallets contact the movable slats at certain points non-uniformly distributed about the slats. As a result, the basic concept of reciprocating floor conveyors with movable slats-having more slats conveying the load than slats being retracted-does not always work to convey pallets and other similar type loads with fixed-form wide bases.
Accordingly, it is an object of the present invention to address the problems associated with conveying palletized loads or the like using reciprocating floor conveyors having a plurality of movable slats. Another object is to improve on the conveyor structures that are disclosed in the aforementioned U.S. Pat. No. 5,588,522 and the aforementioned pending application Ser. No. 08/544,962.
The present invention includes providing at least one lifting slat having a down position, an up position and a top. A fixed position lifting ramp is provided below the top of the lifting slat. The lifting ramp has an upper surface that slopes upwardly from a low end to a high end. A lifting block is positioned on the lifting ramp, vertically between the lifting ramp and the top of the lifting slat. The lifting block has a sloping bottom surface. corresponding in slope to the top surface of the lifting ramp. The lifting block has a top surface that is substantially parallel to the top of the lifting slat when the sloping bottom surface of the lifting block in on the sloping top surface of the lifting ramp. A longitudinally reciprocating drive member is provided. It includes at least one abutment that is movable against the lifting block as the drive member moves in a first direction, for forcing the lifting block up the lifting ramp, so as to cause the lifting block to push upwardly on the lifting slat and move it upwardly into its up position. The drive member also includes at least one other abutment that when the drive member is reversed is movable against the lifting block for forcing the lifting block down the lifting ramp, allowing the lifting slat to drop downwardly into its down position.
According to another aspect of the invention, the lifting block further includes a pair of sidewalls which depend downwardly from the bottom surface outwardly adjacent the opposite sides of the lifting ramp.
In one embodiment of the invention, the drive frame has a pair of longitudinally extending side members that are positioned outwardly of both the lifting ramp and the lifting block and interconnecting transverse members. Each side member includes a pair of inwardly projecting abutments defining between them a space in which a side portion of the lifting block is received. The lifting block may have a pair of opposite side portions which depend from the sloping lower surface of the block into positions that are laterally outwardly from side boundaries of the lifting ramp, laterally inwardly from the longitudinal portions of the drive frame, and longitudinally between the two abutments that project inwardly from the side members of the drive frame.
The lifting ramp may be constructed from metal and the lifting block may be constructed from a self-lubricated plastic material such that the lifting block acts as a bearing both where it contacts the ramp and where it is contacted by the lifting slat.
According to another aspect of the invention, the conveyor includes a base frame below the drive frame and the lifting ramp. The lifting ramp is secured to the base frame. A self-lubricated plastic bearing is positioned vertically between the drive frame and the base frame for facilitating sliding movement of the drive frame relative to the base frame.
In a second embodiment, the lifting ramp may include two laterally spaced apart side parts, each having an upper surface that slopes upwardly from a low end to a high end. A lifting block is positioned on the lifting ramp side parts, vertically between the lifting ramp side parts and the top of the lifting slat. The lifting block has a sloping bottom surface on each of its sides corresponding in slope to the upper surfaces of the lifting ramp side parts. It also has a top surface that is substantially parallel to the top of the lifting slat when the sloping bottom surfaces of the lifting block are on the sloping top surfaces of the lifting ramp side parts. In this embodiment, a longitudinally reciprocating drive member is provided. It includes at least one abutment that is movable against the lifting block as the drive member moves in a first direction, for forcing the lifting block up the lifting ramp, so as to cause the lifting block to push upwardly on the lifting slat and move it upwardly into its up position. The drive member also includes at least one other abutment that when the drive member is reversed is movable against the lifting block for forcing the lifting block down the lifting ramp, allowing the lifting slat to drop downwardly into its down position.
In the second embodiment, the lifting block may comprise a top portion that includes the sloping bottom surfaces and the top surface. It may further include a pair of vertical walls that depend downwardly from the top portion on opposite sides of the drive member and inwardly adjacent the side parts of the lifting ramp. In this embodiment, the drive member may be a longitudinal member that is positioned between the side parts of the lifting ramp. It may be provided with a pair of outwardly projecting abutments forwardly of the lifting block and another pair of outwardly projecting abutments rearwardly of the lifting block. The abutments move in a space that is laterally between the side parts of the lifting ramp. As in the earlier embodiment, the lifting ramp may be constructed from metal and the lifting block may be constructed from a self-lubricated plastic material such that the lifting block acts as a bearing.
The invention also includes a conveyor construction composed of a plurality of lifting slats and a plurality of conveying slats. The conveying slats are mounted and driven to reciprocate back and forth in a common plane. The lifting slats are movable up and down relative to this plane. When the lifting slats are in their xe2x80x9cdownxe2x80x9d position, their top surfaces are below the top surfaces of the conveying slats. A load on the conveyor will be supported solely on the conveying slats. Movement of the conveying slats in a conveying direction will move the load with them in the conveying direction. When the lifting slats are in their xe2x80x9cupxe2x80x9d position, they lift the load up off of the conveying slats. This allows the conveying slats to be retracted to a start position while the load is supported above them by the lifting slats.